Method and apparatus for automated optimization of white and color balance on video camera

ABSTRACT

An image of an optical target including dark and light monochromatic patches is captured. An average YUV value is calculated from a predetermined number of YUV values for each monochromatic patch. A white balance is performed using the averaged YUV values and a predetermined reference image. Each averaged YUV value is converted to an equivalent RGB value. A difference in RGB values between the light and the dark monochromatic patches produces a dynamic range for the RGB values. The dynamic range for the G value is adjusted to match the dynamic range for a G′ value of the predetermined reference image.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The field of the invention is calibration of a video capture device,more specifically the present invention is a method and an apparatus forautomated optimization of white and color balance on a video camera.

(2) Related Art

Presently available video cameras are often equipped with various manualcalibration features including white balance which allows the manualcalibration of white images. Lighting is an important factor in theprocess of accurate video capture of clear white and color balancedimages. Typically, when a video camera is turned on in an arbitrarylighting environment, the target captured by the video camera may not beperceived in the correct color. For example, whites may not be perceivedas white and human faces may be captured with a slight green tint.

There are various disadvantages inherent in the video capture method ofprior art technology. For example, presently available video cameras aretypically equipped with manual white balancing function which adjusts“white” targets captured by a video camera and fine tunes the “white”into a more realistic shade of white. Unfortunately, it is difficult tocorrectly perform manual white balance due to the operator judgment andintervention required to set color controls. Furthermore, the manualwhite balancing function of prior art is catered to adjusting white anddoes not necessarily work for adjusting colors. Additionally, an autowhite balancing function available in some video cameras may work poorlysince no white reference is provided for the video camera to make thewhite color adjustment.

It is therefore desirable to provide an automatic method and apparatusto calibrate white as well as color for targets captured by a videocamera.

BRIEF SUMMARY OF THE INVENTION

A method for optimizing white and color balance on a video capturedevice is disclosed. The method comprises the steps of capturing animage of an optical target through the video capture device andcalibrating the captured image using a predetermined reference imagehaving desired white and color parameters. The calibration results inthe captured image matching the predetermined reference image.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary system block diagram of the present invention.

FIG. 2 is an exemplary optical target used by the present invention inadjusting white and color balance.

FIG. 3 is a table illustrating derivation of YUV color and whiterepresentation as derived from standard RGB color.

FIG. 4 is a flow diagram illustrating the general steps followed by thepresent invention in performing image recognition and data extractionfrom an optical target prior to performing white and color balance.

FIGS. 5a-5 c are flow diagrams illustrating the general steps followedby the present invention in performing white and color balance of atarget image.

FIG. 6 is a block diagram of an exemplary video camera receiving gainand offset values from a computer.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a method and an apparatus for optical targetand calibration software for automated optimization of color balance onvideo cameras. The present invention uses an optical target incombination with calibration software capable of recognizing the opticaltarget. The calibration software adjusts the camera until the perceivedimage matches the correct image available to the calibration software.More specifically, the optical target includes both white and non-whitecolors of known intensity. Since the calibration software has knowledgeof the correct appearance of the optical target, the calibrationsoftware is capable of adjusting the video camera's response such thatthe image observed matches the image's known characteristics. Oncehaving been adjusted for a given light condition, any other objects thenobserved under the same lighting conditions will appear in their trueand accurate colors as captured by the video camera.

The present invention may reduce operator intervention. Further, thepresent invention may automatically align the observed image of theoptical target with a stored reference image and adjusts for a minimumdifference between the observed image and the reference image.

FIG. 1 is an exemplary illustration of the system of the presentinvention. A personal computer (PC) 103 is coupled to a video camera102. The video camera 102 is directed to an optical target 100 with a Y,U, V color chart optimized for image recognition and a gray backgrounddenoted by hatching.

More specifically, Y represents luminance, separate from color, anddenotes a brightness scale somewhere between black and white. U and Vare color difference values describing colors. A more detailedspecification of the Y, U, V color representation may be found inRecommendation ITU-R BT.601-4, Encoding Parameters of Digital Televisionfor Studios, International Telecommunications Union, published in 1994.

The computer 103 is further coupled to a display device 104 such as acomputer monitor to display the optical target as captured by the videocamera and an input device (not shown) such as a keyboard and/or mouseallowing a user to initiate the automatic color and white balance usingthe present invention's image recognition 112 and calibration 114mechanisms. The image recognition mechanism 112 and calibrationmechanism 114 reside in a storage element 110 which is coupled to aprocessor 106 by a bus 108. The calibration mechanism 114 has a whitebalancer 116, a color balancer 118 and a YUV-RGB converter 120 all usedin automatically calibrating the video capture device 102.

The processor 106 runs the image recognition mechanism 112 and thecalibration mechanism 114 upon initiation of the mechanisms by a userinput through a graphic user interface (GUI) (not shown). Given thedetailed description of the present invention provided herein, a personskilled in the art would be able to generate a GUI suitable to initiatethe image recognition and calibration mechanisms 112 and 114,respectively, of the present invention.

The image recognition mechanism 112 and the calibration mechanism 114 ofthe present invention may also reside in a remote storage elementcoupled to the computer 103 for example through a network such as a widearea network (WAN) or a local area network (LAN).

FIG. 2 is an exemplary reference image which is compared to theperceived image of the optical target. The optical target perceived bythe video camera is identical in format and actual white and colorconfiguration as its corresponding reference image. Any deviation iscreated by the video camera's inaccurate perception of the white andcolor values of the optical target. Additionally, as was shown in FIG.1, the optical target has a background such as gray which separates eachpatch in the target. As will be described later, the background is onlynecessary for the image recognition mechanism of the present inventionin distinguishing and ultimately identifying each patch in the opticaltarget and is not necessary to perform the comparison between theperceived optical target and the reference image. Thus, the backgroundis irrelevant in the case of the reference image illustrated in FIG. 2.

With the present invention, a video capture device first captures animage of the optical target. The video capture device then aligns itsframe against the optical target by utilizing an image recognitionmechanism to recognize that there are 5 columns of patches (or 5 rows ofpatches) at an equal distance from each other. Once the video cameraframe is properly aligned with the optical target, the video capturedevice and the present invention's calibration mechanism is ready tocalibrate the white and color balance of any image under the samelighting.

The present invention's calibration mechanism has access to a “perfect”copy of the optical target as represented in numerics of Y, U, V valuesalso referred herein as a reference image. The optical target ascaptured by the video camera is then compared against the referenceimage by the calibration mechanism to calibrate the video capturedevice.

More specifically, a reference image 200 is an array of 25 rectangleshaving Y, U, V values depicting various specially selected colors. Thereference image 200 (as is the optical target) represents a bit-mapwhere each color unit (pixel) may be located in an X-Y axisconfiguration.

The exemplary reference image specifies varying YUV values for eachpatch. From left to right, row 1 patch 1 contains the CCIR-601specification defined legal minimum for Y (luminance). Row 1 patch 2contains a Y value which is half-way between CCIR-601 specificationdefined minimum and median. Row 1 patch 3 contains a Y value which is aCCIR-601 specification defined median. Row 1 patch 4 contains a Y valuewhich is half-way between CCIR-601 specification defined median andmaximum values. Finally, Row 1 patch 5 contains a Y value which is aCCIR-601 specification defined maximum. The Y values are defined as suchall while holding U and V values at 128 which is neutral and representsno color. The U and V values are held at 128 for setting the gain andoffset of Y, without interaction from the U and V color differencevalues.

Rows 2 and 3 are tailored to exercise the U color channel only, exceptfor column 3, which sets the color vector to 315 degrees and 135degrees, respectively. The vectors in column 3 are chosen to bisect the+U, −V and the −U, +V axis, providing a good linearity check for color.In row 3, the U channel sequentially assumes the following values: patch1 has a U value which is near the CCIR-601 specification-defined legalminimum, patch 2 has a U value which is half-way between the CCIR-601specification defined minimum and median values, patch 3 has a U valuewhich sets the color vector to 135 degrees, patch 4 has a U value whichis half-way between the CCIR-601 specification defined median andmaximum values, and patch 5 has a U value near the CCIR-601specification defined maximum legal value. The U values are defined allwhile holding the V value at 128 (except for column 3), and ensuringthat the corresponding R, G, or B values do not saturate beyond legalbounds in their equivalent color space. The table in FIG. 3 describesthe YUV to RGB relationships as defined in CCIR-601 in more detail.

The resulting values of the Y values from row 3 are used in row 2 whichhas monochromatic patches (except for column 3). The row 2 monochromaticpatches provide luminance linearity references. More specifically,luminance is a linear function and the degree of luminance may beverified by checking multiple points along the line as defined by thelinear function. Here, the monochromatic patches are the referencepoints which may be used to verify luminance.

Rows 4 and 5 are tailored to exercise the V color channel only, exceptfor column 3, which sets the color vector to 45 degrees and 225 degrees,respectively. The vectors in column 3 are chosen to bisect the +U, +Vand the −U, −V axis, providing another good linearity check for color.In row 5, the V color channel sequentially assumes the following values:patch 1 has a V value near the CCIR-601 specification-defined legalminimum, patch 2 has a V value half-way between the CCIR-601 minimum andmedian, patch 3 has a V value which sets the color vector to 225degrees, patch 4 has a V value which is half-way between the CCIR-601median and maximum values, and patch 5 has a V value near the CCIR-601maximum legal value.

The V values are set while holding U at 128 (except for column 3), andensuring that the corresponding R, G or B values do not saturate beyondlegal bounds in their equivalent color space. The resulting values of Yfrom row 5 are used in row 4, which has monochromatic patches (exceptfor column 3). The monochromatic patches provide more luminancelinearity references.

Other suitable optical targets with varying configurations of YUV and/orRGB values may be realized by a person skilled in the art given thedetailed description provided herein.

FIG. 3 is a table illustrating the generation of a YUV color and whiterepresentation derived from the CCIR-601 RGB color and white standard.More specifically, the table illustrates the algorithm utilized by thecalibration mechanism 114 in performing conversions 300 between YUV andRGB values. The conversion if performed when determining offset and gainvalues to be provided to the video camera for calibration of theperceived white and color values to match the “perfect” copy of theoptical target (i.e. the reference image).

In the illustrated exemplary conversion method, it is assumed that YUVis CCIR-601 compliant. Further, the given method is exemplary for RGBvalues having a range of 0 to 255, Y value having a range of 16 to 235and U and V values having a range of 16 to 240.

FIG. 4 is a flow diagram illustrating the general steps followed by thepresent invention in performing image recognition and data extractionfrom the optical target using the image recognition mechanism of thepresent invention. As was illustrated in FIG. 1, an optical target isplaced such that the optical target fills the video camera's field ofview with all given color patches and the surrounding gray backgroundvisible on a monitor coupled to the video camera. The black patch may beoriented in any of the corners of the optical target. The calibrationsoftware is then invoked on a computer coupled to the video camera andthe monitor. Precise alignment of the optical target with the videocamera is unnecessary since the present invention will find a cluster ofpixels from the center of each patch as it identifies the patches byimage recognition.

More specifically, in step 401, the image recognition mechanism of thepresent invention scans across successive horizontal lines of theoptical target captured by the video camera beginning from the top ofthe optical target. In step 402, contrast transitions indicative of atransition between the background to the patches are noted from line toline and the top edge of the first row of patches is identified. Thebackground surrounds all patches on the optical target. The contrasttransitions are sudden changes in luminance between patches and thebackground.

The image recognition mechanism then scans successive lines to discernthe horizontal structure on the optical target by counting the top edgesof each patch, or contrast transitions across horizontal lines andnoting that there are five differing wide regions (patches) which areseparated by the background. In step 403, successive lines on thecaptured optical target is scanned and left and right edges (bounds) ofeach patch are identified by noting the contrast transitions. In step404, once the left and right bounds of the patches are identified, thecenter of each patch on an X-axis is calculated For example, the centerof a patch on the X-axis may be calculated by subtracting the X-axisvalue of the left edge of a patch from the X-axis value of the rightedge of the patch and dividing the result by two. In step 405, theprocess is repeated for consecutive horizontal lines until the bottomedge of the top row of patches is reached where the horizontaltransitions are no longer seen while the interposing background is beingscanned.

In step 406, once the top and bottom bounds of the patches areidentified, the location of the center of each patch on the Y-axis iscalculated. For example, the center of a patch on the Y-axis may becalculated by subtracting the Y-axis value of the bottom edge of a patchfrom the Y-axis value of the top edge of the patch and dividing theresult by two.

In step 407, after continuing the scan process for several moresuccessive horizontal lines (the height of the background strip betweenrows of patches), additional contrast transitions are again noted fromline to line when the top edge of the second row of patches is scanned.The process is repeated until the left, right, top and bottom boundariesof each row of patches are identified and the center of each patch onthe X-axis and the Y-axis are determined.

Since vertical, horizontal and rotational alignment of the opticaltarget and the video camera will likely be imperfect, the exact edgeplacement of the patches as discerned by the image recognition mechanismwill not constitute precise horizontal rows of patches and verticalcolumns of patches. Consequently, the transitions within a given scanline from within a background boundary to within, for example, fivepatches, may occur over several scan lines in numbers of incrementsproportional to the rotational skew of the optical target versus thevideo camera. The present invention's image recognition approach isintentionally tolerant of these issues since it uses only the greatestobserved X and Y extents for each patch and then calculates to find thecenter of each patch.

In step 408, an array of pixels from the center of each patch issampled. For example, a 4×4 array of 16 pixels are sampled. In step 409,the bit values of the pixels representative of YUV values for each patchare then averaged. The resulting averaged YUV values one for each patchrepresent the pre-calibrated response of the video camera to thestimulus of the optical target.

FIGS. 5a-5 c are flow diagrams illustrating the general steps followedby the present invention in performing the white and color balance. YUVas referred in FIG. 5 and 6 and the accompanying detailed description isthe raw, uncorrected data as perceived by the video camera from theoptical target, and Y′U′V′ is the gain and offset compensation to theYUV necessary to make them correct.

In step 501, execution of the white balancer of the calibrationmechanism is initiated. By convention, white balance must be performedin the RGB (red, green and blue) color space. More specifically, whitebalance requires calibration of the G value for white. Additionally, theR and B values must be comparatively calibrated against the G value. Thecalibration mechanism of the present invention must therefore eithercalculate R′G′B′ from the Y′U′V′ it obtains from the video camera or adecoder, or use a given R′G′B′ directly if the R′G′B′ is supplieddirectly. This YUV to RGB conversion is illustrated in FIG. 6'scalibration adjustment and color space conversion matrices.

In step 502, the Y, U and V gain settings are initialized by being setto a nominal value. More specifically, gain is a multiplicative scalefactor ranging, for example, from 0.5 to 1.5 used in adjusting rawuncorrected YUV values. A nominal value for a gain setting ranging from0.5 to 1.5 is 1.0. In step 503, the corresponding offset controls areset to zero. More specifically, offset is an additive correction valueadded to the raw YUV values and ranges from −20 to +20. The nominal ordefault value for an offset is 0.

In step 504, the lightest monochromatic patch is examined and its greenvalue is noted by the calibration mechanism. In step 505, the darkestmonochromatic patch is examined and its green value is noted. In step506, the difference in the green values between the lightestmonochromatic patch and the darkest monochromatic patch is obtainedresulting in a dynamic range of the color green.

In step 507, the red (R) and blue (B) values of the lightest and darkestmonochromatic patches are measured as was done for the green (G) valueand their differences are computed to produce a dynamic range of red andblue values. In step 508, the red gain is then set such that theresulting dynamic range of the red value from the lightest to thedarkest monochromatic patches matches the dynamic range of the greenvalue. In this way, the red, green and blue values are balanced suchthat white appears white and colors appear in their correct image. Instep 509, similarly, the blue gain is set such that its resultingdynamic range from the lightest to the darkest monochromatic patchesmatches the dynamic range of the green value.

As was described earlier, a gain is a multiplicative scale factorranging, for example, from 0.5 to 1.5 used in adjusting raw uncorrectedYUV values. Once the dynamic ranges of red and blue values aredetermined, the gain may be determined by generating a multiplicativescale factor which when multiplied with the dynamic ranges of the redand blue values results in the dynamic range of the green value. Forexample, the following depicts an exemplary generation of the gain forthe red value of a given patch:

gain for R=dynamic range of G/dynamic range of R.

In step 510, if the red and blue gains do not have enough range to matchthe green value in dynamic range, for example, due to saturation from Y,U or V gain or offset errors, the second darkest and the second lightestmonochromatic patches are used as bounds for measuring a dynamic rangefor the red and blue values. For example, the second darkest patch inthe optical target illustrated in FIG. 2 is in the second row, fifthcolumn, and the second lightest patch is in the second row, firstcolumn. The process of determining the gain red and blue values arerepeated for successively lighter and darker patches until the dynamicrange of the red and blue values match those of the green value. Oncethe white balance has been calibrated in this way, the execution of thecolor balancer of the calibration mechanism performs the color balancebeginning with determining the Y′ gain.

In step 511, the lightest and the darkest monochromatic patches areexamined with the benefit of the correct white balance. In step 512 theobserved dynamic range of Y′ from the lightest to the darkestmonochromatic patches is compared with the pre-determined dynamic rangeof the corresponding patches on the reference image. In step 513, the Y′gain is adjusted such that the dynamic ranges between the observedoptical target and reference image match. In step 514, the Y′ offset isadjusted such that the absolute values of Y′ match the reference valuesshown in the chart for both light and dark patches.

Next, the U′ gain is calibrated. In step 515, the patches having thehighest and lowest levels of U′ are examined with the benefit of thecorrect white balance. In step 516, the observed dynamic range of U′from the highest and lowest levels of U′ patches is compared with thepre-determined dynamic range of the corresponding patches on thereference image. In step 517, the U′ gain is adjusted such that thedynamic ranges between the observed target and the reference imagematch. In step 518, the U′ offset is adjusted such that U′ is set to 128(neutral=no color) when all of the top row of monochromatic patches isexamined.

Next, the V′ gain is calibrated. In step 519, the patches having thehighest and lowest levels of V′ are examined with the benefit of thecorrect white balance. In step 520, the observed dynamic range of V′from the highest and lowest levels of V′ patches is compared with thepre-determined dynamic range of the corresponding patches on thereference image. In step 521, the V′ gain is adjusted by increasing ordecreasing the gain such that the dynamic ranges between the observedtarget and the reference optical target match. In step 522, the V′offset is adjusted such that V′ is set to 128 (neutral=no color) whenall of the top row of monochromatic patches is examined. In this way,both the white balance and the color balance are calibrated.

In the illustrated embodiment, to ensure color calibration accuracy, a“best fit” curve fitting approach may be used to minimize linearityerrors at the cost of more computer host-based computing effort.

FIG. 6 illustrates exemplary calibration adjustment and color spaceconversion matrices. The video camera 102 captures an image of theoptical target 100 through an optical sensor 600 and forwards theinformation to the computer 103 running the present invention'scalibration mechanism. The information is converted from RGB to YUVvalues by conversion block 602 and is converted from analog to digitalthrough for example an analog-to-digital converter (ADC) (not shown).The Y′U′V′ values are converted to R′G′B′ by a conversion block 604 inthe computer 103. Once the gain and offset values for the YUV and thecorresponding RGB values are automatically calculated by the computerthrough the calibration mechanism 114, the gain and offset values areforwarded to the video camera 102 after they are converted from digitalto analog form through for example a digital-to-analog converter (DAC)(not shown). The video camera 102 then utilizes the gain and offsetvalues to calibrate its white and color perception under the givenlighting. The method by which a video camera calibrates white and colorperception once gain and offset values are provided is well known in theart and needs no further explanation.

What has been described is a method and apparatus for automaticallycalibrating a video capture device given an optical target with aplurality of white and color patches. Once the video capture deviceperceives an image of the optical target, an image recognition mechanismidentifies the perceived image. The identified image is then compared toa “perfect” copy of the optical target (also referred herein as areference image). The calibration mechanism then determines gain andoffset values for each patch. The gain and offset values generated willcalibrate the video capture device to have a perception of the opticaltarget which matches the reference image. Once generated, the gain andoffset values are forwarded to the video capture device to complete thecalibration process.

While certain exemplary embodiments have been described in detail andshown in the accompanying drawings, it is to be understood that suchembodiments are merely illustrative of and not restrictive on the broadinvention, and that this invention is not to be limited to the specificarrangements and constructions shown and described, since various othermodifications may occur to those with ordinary skill in the art.

What is claimed:
 1. A method for calibrating a video capture devicecomprising: capturing an image of an optical target that includes a darkmonochromatic patch having a YUV color value with a Y value less than amedian Y value and a light monochromatic patch having a YUV color valuewith a Y value greater than the median Y value, each monochromatic patchhaving U and V values that are neutral; taking a predetermined number ofYUV values from each monochromatic patch; calculating an average YUVvalue for each monochromatic patch; performing white balance using theaveraged YUV values and a predetermined reference image; converting eachaveraged YUV value to an equivalent RGB value; taking a difference inRGB values between the light monochromatic patch and the darkmonochromatic patch to produce a dynamic range for the RGB values; andadjusting the dynamic range for the G value to match the dynamic rangefor a G′ value of the predetermined reference image.
 2. The method ofclaim 1 further comprising performing image recognition on the opticaltarget to recognize each monochromatic patch.
 3. The method of claim 1wherein the optical target further includes additional monochromaticpatches having neutral values for U and V and Y values less than the Yvalue of the light monochromatic patch and greater than the Y value ofthe dark monochromatic patch, the method further comprising taking asecond difference between successively lighter a and darkermonochromatic patches until the second difference is capable of matchingthe dynamic range of the corresponding patches on the predeterminedreference image.
 4. The method of claim 1 further comprising determiningwhether the dynamic ranges of the R and B values match the dynamic rangeof the G value.
 5. The method of claim 4 wherein the optical targetfurther includes additional monochromatic patches having neutral valuesfor U and V and Y values less than the Y value of the lightmonochromatic patch and greater than the Y value of the darkmonochromatic patch, the method further comprising taking the differencein R and B values of successive lighter and darker monochromatic patchesuntil the dynamic ranges of said R and B values are capable of matchingthe dynamic range of said G value.
 6. The method of claim 5 furthercomprising calculating a gain value for the R and B values to match thedynamic range of the R and B values to the dynamic range of the G value.7. The method of claim 6 further comprising calculating a gain and anoffset for the Y value to match the dynamic range of the Y value to thedynamic range of the corresponding patches on the predeterminedreference image.
 8. The method of claim 1 wherein the optical targetfurther includes: a first U calibration patch having a YUV color valuewith a U value less than a median U value, a Y value chosen such thatresulting R, G, and B values are valid, and a V value that is neutral;and a second U calibration patch having a YUV color value with a U valuegreater than a median U value, a Y value chosen such that resulting R,G, and B values are valid, and a V value that is a neutral; the methodfurther comprising: taking the difference in U values between the firstU calibration patch and the second U calibration patch to produce adynamic range for the U value; and adjusting a gain for the U value tomatch the dynamic range for the U value to the corresponding dynamicrange in the predetermined reference image.
 9. The method of claim 8wherein the optical target further includes: a third U calibration patchhaving a YUV color value with a Y value equal to the Y value of thefirst U calibration patch, and U and V values that are neutral; and afourth U calibration patch having a YUV color value with a Y value equalto the Y value of the second U calibration patch, and U and V valuesthat are neutral; the method further comprising verifying the luminancewith the third and fourth U calibration patches.
 10. The method of claim8 wherein the optical target further includes: a first V calibrationpatch having a YUV color value with a V value less than a median Vvalue, a Y value chosen such that resulting R, G, and B values arevalid, and a U value that is neutral; and a second V calibration patchhaving a YUV color value with a V value greater than a median V value, aY value chosen such that resulting R, G, and B values are valid, and a Uvalue that is neutral; the method further comprising: taking thedifference in V values between the first V calibration patch and thesecond V calibration patch to produce a dynamic range for the V value;and adjusting a gain for the V value to match the dynamic range for theV value to the corresponding dynamic range In the predeterminedreference image.
 11. The method of claim 10 wherein the optical targetfurther includes: a third V calibration patch having a YUV color valuewith a Y value equal to the Y value of the first V calibration patch,and U and V values that are neutral; and a fourth V calibration patchhaving a YUV color value with a Y value equal to the Y value of thesecond V calibration patch, and U and V values that are neutral; and themethod further comprising verifying the luminance with the third andfourth V calibration patches.
 12. The method of claim 10 wherein theoptical target further includes: a first color calibration patch havinga YUV color value which sets the color vector to 135 degrees; a secondcolor calibration patch having a YUV color value which sets the colorvector to 315 degrees; a third color calibration patch having a YUVcolor value which sets the color vector to 45 degrees; and a fourthcolor calibration patch having a YUV color value which sets the colorvector to 225 degrees; and the method further comprising verifying colorlinearity with the first, second, third, and fourth color calibrationpatches.
 13. An apparatus for video calibration comprising: a videocapture device configured to capture an image of an optical target thatIncludes a dark monochromatic patch having a YUV color value with a Yvalue less than a median Y value and a light monochromatic patch havinga YUV color value with a Y value greater than the median Y value, eachmonochromatic patch having U and V values that are neutral; a samplingdevice configured to take a predetermined number of YUV values from eachmonochromatic patch; an arithmetic device configured to calculate anaverage YUV value for each monochromatic patch: a white balance deviceconfigured to perform white balance using the averaged YUV values and apredetermined reference image; a conversion block configured to converteach averaged YUV value to an equivalent RGB value; a second arithmeticdevice configured to adjust the dynamic range for the G value to matchthe dynamic range for a G′ value of the is predetermined referenceimage.
 14. The apparatus of claim 13 further comprising an imagerecognition device configured to recognize each monochromatic patch onthe optical target.
 15. The apparatus of claim 13 wherein the opticaltarget further includes additional monochromatic patches having neutralvalues for U and V and Y values less than the Y value of the lightmonochromatic patch and greater than the Y value of the darkmonochromatic patch, the apparatus further comprising a third arithmeticdevice configured to take a second difference between successivelylighter and darker monochromatic patches until the second difference iscapable of Matching the dynamic range of the corresponding patches onthe predetermined reference image.
 16. The apparatus of claim 13 furthercomprising a matching device configured to determine whether the dynamicranges of the R and B values match the dynamic range of the G value. 17.The apparatus of claim 16 wherein the optical target further includesadditional monochromatic patches having neutral values for U and V and Yvalues less than the Y value of the light monochromatic patch andgreater than the Y value of the dark monochromatic patch, the apparatusfurther comprising a third arithmetic device configured to take thedifference in R and B values of successive lighter and darkermonochromatic patches until the dynamic ranges of said R and B valuesare capable of matching the dynamic range of said G value.
 18. Theapparatus of claim 17 further comprising a fourth arithmetic deviceconfigured to calculate a gain value for the R and B values to match thedynamic range of the R and B values to the dynamic range of the G value.19. The apparatus of claim 18 further comprising a fifth arithmeticdevice configured to calculate a gain and an offset for the Y value tomatch the dynamic range of the Y value to the dynamic range of thecorresponding patches on the predetermined reference image.
 20. Theapparatus of claim 13 wherein the optical target further includes: afirst U calibration patch having a YUV color value with a U value lessthan a median U value, a Y value chosen such that resulting R, G, and Bvalues are valid, and a V value that is neutral; and a second Ucalibration patch having a YUV color value with a U value greater than amedian U value, a Y value chosen such that a resulting R, G, and Bvalues are valid, and a V value that is neutral; the apparatus furthercomprising: a third arithmetic device configured to take the differencein U values between the first U calibration patch and the second Ucalibration patch to produce a dynamic range for the U value; and afourth arithmetic device configured to adjust a gain for the U value tomatch the dynamic range for the U value to the corresponding dynamicrange in the predetermined reference image.
 21. The apparatus of claim20 wherein the optical target further includes: a third U calibrationpatch having a YUV color value with a Y value equal to the Y value ofthe first U calibration patch, and U and V values that are neutral; anda fourth U calibration patch having a YUV color value with a Y valueequal to the Y value of the second U calibration patch, and U and Vvalues that are neutral; and the apparatus further comprising a verifierconfigured to verify the luminance with the third and fourth Ucalibration patches.
 22. The apparatus of claim 20 wherein the opticaltarget further includes: a first V calibration patch having a YUV colorvalue with a V value less than a median V value, a Y value chosen suchthat resulting R, G, and B values are valid, and a U value that isneutral; and a second V calibration patch having a YUV color value witha V value greater than a median V value, a Y value chosen such thatresulting R, G, and B values are valid, and a U value that is neutral;the apparatus further comprising: a fifth arithmetic device configuredto take the difference In V values between the first V calibration patchand the second V calibration patch to produce a dynamic range for the Vvalue; and a sixth arithmetic device configured to adjust a gain for theV value to match the dynamic range for the V value to the correspondingdynamic range in the predetermined reference image.
 23. The apparatus ofclaim 22 wherein the optical target further includes: a third Vcalibration patch having a YUV color value with a Y value equal to the Yvalue of the first V calibration patch, and U and V values that areneutral; and a fourth V calibration patch having a YUV color value witha Y value equal to the Y value of the second V calibration patch, and Uand V values that are neutral; the apparatus further comprising averifier configured to verify the luminance with the third and fourth Vcalibration patches.
 24. The apparatus of claim 22 wherein the opticaltarget further includes: a first color calibration patch having a YUVcolor value which sets the color vector to 135 degrees; a second colorcalibration patch having a YUV color value which sets the color vectorto 315 degrees; third color calibration patch having a YUV color valuewhich sets the color vector to 45 degrees; and a fourth colorcalibration patch having a YUV color value which sets the color vectorto 225 degrees; and the apparatus further comprising a verifierconfigured to verify color linearity with the first, second, third, andfourth color calibration patches.
 25. A storage medium having storedtherein a plurality of programming instructions designed for executionby a processor, wherein when executed, the programming instructionscalibrates a video capture device, said storage medium comprising: animage module, execution of said image module configured to e receive animage of an optical target that includes a dark monochromatic patchhaving a YUV color value with a Y value less than a median Y value and alight monochromatic patch having a YUV color value with a Y valuegreater than the median Y value, each monochromatic patch having U and Vvalues that are neutral; a sampling module, execution of said samplingmodule configured to take a predetermined number of YUV values from eachmonochromatic patch; a white balance module, execution of said whitebalance module configured to perform white balance using the averagedYUV values and a predetermined reference image; a conversion module,execution of said conversion module configured to convert each averagedYUV value to an equivalent RGB value; a second arithmetic module,execution of said second arithmetic module configured to adjust thedynamic range for the G value to match the dynamic range for a G′ valueof the predetermined reference image.
 26. The storage medium of claim 25further comprising an image recognition module, execution of said imagerecognition module configured to recognize each monochromatic patch onthe optical target.
 27. The storage medium of claim 25 wherein theoptical target further includes additional monochromatic patches havingneutral values for U and V and V values less than the Y value of thelight monochromatic patch and greater than the Y value of the darkmonochromatic patch, the storage medium further comprising a thirdarithmetic module, execution of said third arithmetic module configuredto take a second difference between successively lighter and darkermonochromatic patches until the second difference is capable of matchingthe dynamic range of the corresponding patches on the predeterminedreference image.
 28. The storage medium of claim 25 further comprising amatching module, execution of said matching module configured todetermine whether the dynamic ranges of the R and B values match thedynamic range of the G value.
 29. The storage medium of claim 28 whereinthe optical target further includes additional monochromatic patcheshaving neutral values for U and V and Y values less than the Y value ofthe light monochromatic patch and greater than the Y value of the darkmonochromatic patch, the storage medium further comprising a thirdarithmetic module, execution of said third arithmetic module configuredto take the difference in R and B values of successive lighter anddarker monochromatic patches until the dynamic ranges of said R and Bvalues are capable of matching the dynamic range of said G value. 30.The storage medium of claim 29 further comprising a fourth arithmeticmodule, execution of said fourth arithmetic module configured tocalculate a gain value for the R and B values to match the dynamic rangeof the R and B values to the dynamic range of the G value.
 31. Thestorage medium of claim 30 further comprising a fifth arithmetic module,execution of said fifth arithmetic module configured to calculate a gainand an offset for the Y value to match the dynamic range of the Y valueto the dynamic range of the corresponding patches on the predeterminedreference image.
 32. The storage medium of claim 25 wherein the opticaltarget further includes: a first U calibration patch having a YUV colorvalue with a U value less than a median U value, a Y value chosen suchthat resulting R, G, and B values are valid, and a V value that isneutral; and a second U calibration patch having a YUV color value witha U value greater than a median U value, a Y value chosen such thatresulting R, G, and B values are valid, and a V value that is neutral;the storage medium further comprising; a third arithmetic module,execution of said third arithmetic module configured to take thedifference in U values between the first U calibration patch and thesecond U calibration patch to produce a dynamic range for the U value;and a fourth arithmetic module, execution of said fourth arithmeticmodule configured to adjust a gain for the U value to match the dynamicrange for the U value to the corresponding dynamic range In thepredetermined reference image.
 33. The storage medium of claim 32wherein the optical target further includes: a third U calibration patchhaving a YUV color value with a Y value equal to the Y value of thefirst U calibration patch, and U and V values that are neutral; and afourth U calibration patch having a YUV color value with a Y value equalto the Y value of the second U calibration patch, and U and V valuesthat are neutral; the storage medium further comprising a verifiermodule, execution of said verifier module configured to verify theluminance with the third and fourth U calibration patches.
 34. Thestorage medium of claim 32 wherein the optical target further includes:a first V calibration patch having a YUV color value with a V value lessthan a median V value, a Y value chosen such that resulting R, G, and Bvalues are valid, and a U value that is neutral; and a second Vcalibration patch having a YUV color value with a V value greater than amedian V value, a Y value chosen such that resulting R, G, and B valuesare valid, and a U value that is neutral; the storage medium furthercomprising: a fifth arithmetic module, execution of said fiftharithmetic module configured to take the difference in V values betweenthe first V calibration patch and the second V calibration patch toproduce a dynamic range for the V value; and a sixth arithmetic module,execution of said sixth arithmetic module configured to adjust a gainfor the V value to match the dynamic range for the V value to thecorresponding dynamic range in the predetermined reference image. 35.The storage medium of claim 34 wherein the optical target furtherincludes: a third V calibration patch having a YUV color value with a Yvalue equal to the Y value of the first V calibration patch, and U and Vvalues that are neutral; and a fourth V calibration patch having a YUVcolor value with a Y value equal to the Y value of the second Vcalibration patch, and U and V values that are neutral; and the storagemedium further comprising a verifier module, execution of said verifiermodule configured to verify the luminance with the third and fourth Vcalibration patches.
 36. The storage medium of claim 34 wherein theoptical target further includes: a first color calibration patch havinga YUV color value which sets the color vector to 135 degrees; a secondcolor calibration patch having a YUV color value which sets the colorvector to 315 degrees; a third color calibration patch having a YUVcolor value which sets the color vector to 45 degrees; and a fourthcolor calibration patch having a YUV color value which sets the colorvector to 225 degrees; and the storage medium further comprising averifier module, execution of said verifier module configured to verifycolor linearity with the first, second, third, and fourth colorcalibration patches.